The present invention relates to a differential apparatus installed in a four-wheel drive vehicle. More particularly, it relates to a differential apparatus arranged on the side of axles to be operatively separated from the driving force of an engine under a two-wheel driving condition of the vehicle.
The prior art includes a differential apparatus as shown in FIG. 1, which is similar to that disclosed in Japanese Patent Publication (kokai) No. 63-235748.
The differential apparatus 301 is provided, inside a differential casing 303, with a ring 305 which is rotatably arranged therein. A pinion shaft 309 of a bevel-gear type of differential mechanism 307 is connected to ring 305. Further, at the interior of the differential casing 303, a slide gear 311 is arranged to move in the axial direction of the differential casing 303. A dog clutch 313 is formed between the slide gear 311 and the ring 305 of the differential mechanism 307 and connects the differential casing 303 with the ring 305 or disconnects the former from the latter owing to the operation to move the slide gear 311.
A hydraulic actuator 315 disposed outside the differential casing 303 operates to move the slide gear 311 through the intermediary of a shift fork 317 thereby to engage the dog clutch 313. Conversely, when the hydraulic actuator 315 is inactivated, the slide gear 311 returns to the opposite direction by a return spring 319, so that the dog clutch 313 is disengaged.
Under condition that the differential apparatus 301 is installed in the four-wheel drive car, when the dog clutch 313 engages, the vehicle is brought into the four-wheel driving condition. On the other hand, when dog clutch 313 is disengaged, the vehicle is brought into the two-wheel driving condition.
Generally speaking, in a differential apparatus having a clutch for connecting and disconnecting the driving force, if the actuator has any trouble in operation, it is likely that the vehicle cannot travel under four-wheel driving condition. In such a case, it will be impossible for the vehicle to escape from a bad road.
Also, the greater part of traveling period for a four-wheel driving vehicle is occupied in its two-wheel driving state, it has been required to reduce energy consumption during two-wheel driving, if possible.